A fluorine-containing polymer powder is usable as a coating powder material.
The method for producing a fluorine-containing polymer powder disclosed in Patent Literature 1 is spray-drying of an aqueous dispersion prepared by emulsion polymerization.
In the method disclosed in Patent Literature 2, agglomerated powders of tetrafluoroethylene copolymers prepared by emulsion polymerization are thermally fused at a temperature not higher than the melting point. The resulting substance is then subjected to grinding, heat treatment, and separation by cracking to give a tetrafluoroethylene copolymer powder having a specific melt viscosity of 1×104 to 1×106 poise, an average particle size of 5 to 500 μm, a void ratio of at most 0.75, and a total surface area of 0.2 to 20 m2/cm3.
Some fluorine-containing surfactants used in emulsion polymerization are environmentally harmful. Such a fluorine-containing surfactant is left in produced powder particles and further left in a film to be formed therefrom, and therefore is environmentally harmful and impairs the physical properties, such as a non-sticking property, of a fluorine resin film.
The method for producing a fluorine-containing polymer powder disclosed in Patent Literature 3 includes: preparing a granulated substance by granulating fluorine-containing polymer particles prepared by solution polymerization or suspension polymerization, in a granulation medium with stirring; grinding the granulated substance to prepare fluorine-containing polymer particles; and heat-treating the fluorine-containing polymer particles in an atmosphere at a temperature of not lower than the melting point thereof, to melt at least a part of the powder.
The method for producing a fluoropolymer powder disclosed in Patent Literature 4 includes: densifying fluoropolymer base powder with rolls under the conditions that enable the specific gravity of the resulting powder to reach at least 90% of the absolute specific gravity; grinding the resulting powder; removing fine particles within a range of 3 to 40% by weight of the entire particle size distribution by airflow classification; and removing coarse particles within a range of 1 to 20% by weight of the entire particle size distribution.